diff -Naur linux-0.01/boot/boot.s linux-0.01-rm-1.0/boot/boot.s --- linux-0.01/boot/boot.s 1991-09-12 23:10:02.000000000 +0200 +++ linux-0.01-rm-1.0/boot/boot.s 2007-11-13 19:39:14.000000000 +0100 @@ -1,41 +1,41 @@ -| -| boot.s -| -| boot.s is loaded at 0x7c00 by the bios-startup routines, and moves itself -| out of the way to address 0x90000, and jumps there. -| -| It then loads the system at 0x10000, using BIOS interrupts. Thereafter -| it disables all interrupts, moves the system down to 0x0000, changes -| to protected mode, and calls the start of system. System then must -| RE-initialize the protected mode in it's own tables, and enable -| interrupts as needed. -| -| NOTE! currently system is at most 8*65536 bytes long. This should be no -| problem, even in the future. I want to keep it simple. This 512 kB -| kernel size should be enough - in fact more would mean we'd have to move -| not just these start-up routines, but also do something about the cache- -| memory (block IO devices). The area left over in the lower 640 kB is meant -| for these. No other memory is assumed to be "physical", ie all memory -| over 1Mb is demand-paging. All addresses under 1Mb are guaranteed to match -| their physical addresses. -| -| NOTE1 abouve is no longer valid in it's entirety. cache-memory is allocated -| above the 1Mb mark as well as below. Otherwise it is mainly correct. -| -| NOTE 2! The boot disk type must be set at compile-time, by setting -| the following equ. Having the boot-up procedure hunt for the right -| disk type is severe brain-damage. -| The loader has been made as simple as possible (had to, to get it -| in 512 bytes with the code to move to protected mode), and continuos -| read errors will result in a unbreakable loop. Reboot by hand. It -| loads pretty fast by getting whole sectors at a time whenever possible. +; +; boot.s +; +; boot.s is loaded at 0x7c00 by the bios-startup routines, and moves itself +; out of the way to address 0x90000, and jumps there. +; +; It then loads the system at 0x10000, using BIOS interrupts. Thereafter +; it disables all interrupts, moves the system down to 0x0000, changes +; to protected mode, and calls the start of system. System then must +; RE-initialize the protected mode in it's own tables, and enable +; interrupts as needed. +; +; NOTE! currently system is at most 8*65536 bytes long. This should be no +; problem, even in the future. I want to keep it simple. This 512 kB +; kernel size should be enough - in fact more would mean we'd have to move +; not just these start-up routines, but also do something about the cache- +; memory (block IO devices). The area left over in the lower 640 kB is meant +; for these. No other memory is assumed to be "physical", ie all memory +; over 1Mb is demand-paging. All addresses under 1Mb are guaranteed to match +; their physical addresses. +; +; NOTE1 abouve is no longer valid in it's entirety. cache-memory is allocated +; above the 1Mb mark as well as below. Otherwise it is mainly correct. +; +; NOTE 2! The boot disk type must be set at compile-time, by setting +; the following equ. Having the boot-up procedure hunt for the right +; disk type is severe brain-damage. +; The loader has been made as simple as possible (had to, to get it +; in 512 bytes with the code to move to protected mode), and continuos +; read errors will result in a unbreakable loop. Reboot by hand. It +; loads pretty fast by getting whole sectors at a time whenever possible. -| 1.44Mb disks: +; 1.44Mb disks: sectors = 18 -| 1.2Mb disks: -| sectors = 15 -| 720kB disks: -| sectors = 9 +; 1.2Mb disks: +; sectors = 15 +; 720kB disks: +; sectors = 9 .globl begtext, begdata, begbss, endtext, enddata, endbss .text @@ -48,7 +48,7 @@ BOOTSEG = 0x07c0 INITSEG = 0x9000 -SYSSEG = 0x1000 | system loaded at 0x10000 (65536). +SYSSEG = 0x1000 ; system loaded at 0x10000 (65536). ENDSEG = SYSSEG + SYSSIZE entry start @@ -67,48 +67,48 @@ mov ds,ax mov es,ax mov ss,ax - mov sp,#0x400 | arbitrary value >>512 + mov sp,#0x400 ; arbitrary value >>512 - mov ah,#0x03 | read cursor pos + mov ah,#0x03 ; read cursor pos xor bh,bh int 0x10 mov cx,#24 - mov bx,#0x0007 | page 0, attribute 7 (normal) + mov bx,#0x0007 ; page 0, attribute 7 (normal) mov bp,#msg1 - mov ax,#0x1301 | write string, move cursor + mov ax,#0x1301 ; write string, move cursor int 0x10 -| ok, we've written the message, now -| we want to load the system (at 0x10000) +; ok, we've written the message, now +; we want to load the system (at 0x10000) mov ax,#SYSSEG - mov es,ax | segment of 0x010000 + mov es,ax ; segment of 0x010000 call read_it call kill_motor -| if the read went well we get current cursor position ans save it for -| posterity. +; if the read went well we get current cursor position ans save it for +; posterity. - mov ah,#0x03 | read cursor pos + mov ah,#0x03 ; read cursor pos xor bh,bh - int 0x10 | save it in known place, con_init fetches - mov [510],dx | it from 0x90510. + int 0x10 ; save it in known place, con_init fetches + mov [510],dx ; it from 0x90510. -| now we want to move to protected mode ... +; now we want to move to protected mode ... - cli | no interrupts allowed ! + cli ; no interrupts allowed ! -| first we move the system to it's rightful place +; first we move the system to it's rightful place mov ax,#0x0000 - cld | 'direction'=0, movs moves forward + cld ; 'direction'=0, movs moves forward do_move: - mov es,ax | destination segment + mov es,ax ; destination segment add ax,#0x1000 cmp ax,#0x9000 jz end_move - mov ds,ax | source segment + mov ds,ax ; source segment sub di,di sub si,si mov cx,#0x8000 @@ -116,105 +116,105 @@ movsw j do_move -| then we load the segment descriptors +; then we load the segment descriptors end_move: - mov ax,cs | right, forgot this at first. didn't work :-) + mov ax,cs ; right, forgot this at first. didn't work :-) mov ds,ax - lidt idt_48 | load idt with 0,0 - lgdt gdt_48 | load gdt with whatever appropriate + lidt idt_48 ; load idt with 0,0 + lgdt gdt_48 ; load gdt with whatever appropriate -| that was painless, now we enable A20 +; that was painless, now we enable A20 call empty_8042 - mov al,#0xD1 | command write + mov al,#0xD1 ; command write out #0x64,al call empty_8042 - mov al,#0xDF | A20 on + mov al,#0xDF ; A20 on out #0x60,al call empty_8042 -| well, that went ok, I hope. Now we have to reprogram the interrupts :-( -| we put them right after the intel-reserved hardware interrupts, at -| int 0x20-0x2F. There they won't mess up anything. Sadly IBM really -| messed this up with the original PC, and they haven't been able to -| rectify it afterwards. Thus the bios puts interrupts at 0x08-0x0f, -| which is used for the internal hardware interrupts as well. We just -| have to reprogram the 8259's, and it isn't fun. - - mov al,#0x11 | initialization sequence - out #0x20,al | send it to 8259A-1 - .word 0x00eb,0x00eb | jmp $+2, jmp $+2 - out #0xA0,al | and to 8259A-2 +; well, that went ok, I hope. Now we have to reprogram the interrupts :-( +; we put them right after the intel-reserved hardware interrupts, at +; int 0x20-0x2F. There they won't mess up anything. Sadly IBM really +; messed this up with the original PC, and they haven't been able to +; rectify it afterwards. Thus the bios puts interrupts at 0x08-0x0f, +; which is used for the internal hardware interrupts as well. We just +; have to reprogram the 8259's, and it isn't fun. + + mov al,#0x11 ; initialization sequence + out #0x20,al ; send it to 8259A-1 + .word 0x00eb,0x00eb ; jmp $+2, jmp $+2 + out #0xA0,al ; and to 8259A-2 .word 0x00eb,0x00eb - mov al,#0x20 | start of hardware int's (0x20) + mov al,#0x20 ; start of hardware int's (0x20) out #0x21,al .word 0x00eb,0x00eb - mov al,#0x28 | start of hardware int's 2 (0x28) + mov al,#0x28 ; start of hardware int's 2 (0x28) out #0xA1,al .word 0x00eb,0x00eb - mov al,#0x04 | 8259-1 is master + mov al,#0x04 ; 8259-1 is master out #0x21,al .word 0x00eb,0x00eb - mov al,#0x02 | 8259-2 is slave + mov al,#0x02 ; 8259-2 is slave out #0xA1,al .word 0x00eb,0x00eb - mov al,#0x01 | 8086 mode for both + mov al,#0x01 ; 8086 mode for both out #0x21,al .word 0x00eb,0x00eb out #0xA1,al .word 0x00eb,0x00eb - mov al,#0xFF | mask off all interrupts for now + mov al,#0xFF ; mask off all interrupts for now out #0x21,al .word 0x00eb,0x00eb out #0xA1,al -| well, that certainly wasn't fun :-(. Hopefully it works, and we don't -| need no steenking BIOS anyway (except for the initial loading :-). -| The BIOS-routine wants lots of unnecessary data, and it's less -| "interesting" anyway. This is how REAL programmers do it. -| -| Well, now's the time to actually move into protected mode. To make -| things as simple as possible, we do no register set-up or anything, -| we let the gnu-compiled 32-bit programs do that. We just jump to -| absolute address 0x00000, in 32-bit protected mode. - - mov ax,#0x0001 | protected mode (PE) bit - lmsw ax | This is it! - jmpi 0,8 | jmp offset 0 of segment 8 (cs) - -| This routine checks that the keyboard command queue is empty -| No timeout is used - if this hangs there is something wrong with -| the machine, and we probably couldn't proceed anyway. +; well, that certainly wasn't fun :-(. Hopefully it works, and we don't +; need no steenking BIOS anyway (except for the initial loading :-). +; The BIOS-routine wants lots of unnecessary data, and it's less +; "interesting" anyway. This is how REAL programmers do it. +; +; Well, now's the time to actually move into protected mode. To make +; things as simple as possible, we do no register set-up or anything, +; we let the gnu-compiled 32-bit programs do that. We just jump to +; absolute address 0x00000, in 32-bit protected mode. + + mov ax,#0x0001 ; protected mode (PE) bit + lmsw ax ; This is it! + jmpi 0,8 ; jmp offset 0 of segment 8 (cs) + +; This routine checks that the keyboard command queue is empty +; No timeout is used - if this hangs there is something wrong with +; the machine, and we probably couldn't proceed anyway. empty_8042: .word 0x00eb,0x00eb - in al,#0x64 | 8042 status port - test al,#2 | is input buffer full? - jnz empty_8042 | yes - loop + in al,#0x64 ; 8042 status port + test al,#2 ; is input buffer full? + jnz empty_8042 ; yes - loop ret -| This routine loads the system at address 0x10000, making sure -| no 64kB boundaries are crossed. We try to load it as fast as -| possible, loading whole tracks whenever we can. -| -| in: es - starting address segment (normally 0x1000) -| -| This routine has to be recompiled to fit another drive type, -| just change the "sectors" variable at the start of the file -| (originally 18, for a 1.44Mb drive) -| -sread: .word 1 | sectors read of current track -head: .word 0 | current head -track: .word 0 | current track +; This routine loads the system at address 0x10000, making sure +; no 64kB boundaries are crossed. We try to load it as fast as +; possible, loading whole tracks whenever we can. +; +; in: es - starting address segment (normally 0x1000) +; +; This routine has to be recompiled to fit another drive type, +; just change the "sectors" variable at the start of the file +; (originally 18, for a 1.44Mb drive) +; +sread: .word 1 ; sectors read of current track +head: .word 0 ; current head +track: .word 0 ; current track read_it: mov ax,es test ax,#0x0fff -die: jne die | es must be at 64kB boundary - xor bx,bx | bx is starting address within segment +die: jne die ; es must be at 64kB boundary + xor bx,bx ; bx is starting address within segment rp_read: mov ax,es - cmp ax,#ENDSEG | have we loaded all yet? + cmp ax,#ENDSEG ; have we loaded all yet? jb ok1_read ret ok1_read: @@ -296,25 +296,25 @@ ret gdt: - .word 0,0,0,0 | dummy + .word 0,0,0,0 ; dummy - .word 0x07FF | 8Mb - limit=2047 (2048*4096=8Mb) - .word 0x0000 | base address=0 - .word 0x9A00 | code read/exec - .word 0x00C0 | granularity=4096, 386 - - .word 0x07FF | 8Mb - limit=2047 (2048*4096=8Mb) - .word 0x0000 | base address=0 - .word 0x9200 | data read/write - .word 0x00C0 | granularity=4096, 386 + .word 0x07FF ; 8Mb - limit=2047 (2048*4096=8Mb) + .word 0x0000 ; base address=0 + .word 0x9A00 ; code read/exec + .word 0x00C0 ; granularity=4096, 386 + + .word 0x07FF ; 8Mb - limit=2047 (2048*4096=8Mb) + .word 0x0000 ; base address=0 + .word 0x9200 ; data read/write + .word 0x00C0 ; granularity=4096, 386 idt_48: - .word 0 | idt limit=0 - .word 0,0 | idt base=0L + .word 0 ; idt limit=0 + .word 0,0 ; idt base=0L gdt_48: - .word 0x800 | gdt limit=2048, 256 GDT entries - .word gdt,0x9 | gdt base = 0X9xxxx + .word 0x800 ; gdt limit=2048, 256 GDT entries + .word gdt,0x9 ; gdt base = 0X9xxxx msg1: .byte 13,10